Magnetic testing



250-201 AU 252 EX REFERENCE MINER FIPSZIZ XR 199079105 7 y 3 -F. E. HAWORTH 1,907,105

' I IAGIIBIIC 'ras'mm Filed Sept. 30. 1930 2'Sheets-Shee t 1 IN VENTOR by aamwonf ATTORNEY Patented May 2, 1933 PATENTO'FFICE M018 ELWOMH, OI smnu'r, JERSEY, ASSIGNOB '10 BELL TELEPHOIi'E LABORATORIES, IIGJBPOMTED, O l NEW YORK, N. Y2, A (XJB-POBATION O! m YORK memo rns'rmc Application filed September 30, 1880. Serial R0. 485,570.

The present invention relates to testing apparatus and particularly to apparatus for testing and measuring the properties of magnetic materials.

An object of the invention is to provide means for quickly and accurately ascertain- 20 force and the other being connected to a ballistic galvanometer. As the magnetizing force is changed in small steps, the alvanometer needle deflects proportion y to the chan e in' flux. In this manner it is possible,

as by ta ing a large number of readings, to ob-- tain a series of disconnected points enabling the plotting of magnetization or hysteresis curves.- Thisprocedure, however, is tedious, time consuming and inaccurate.

so A somewhat more rapid method of tracing magnetic curves has been described by J. A'. Ewm in Magnetic Induction in Iron and other etals, pages 118 to 123, third edition,

1900. However, this method is applicable.

as only to specimens having the form of bars or laminations. The Braun tube hysteresigraph described in U. S. Patent 1,57 4,350, February 23, 1926, to J. B. Johnson, has the disadvantage of introducing eddy current-effects in 40' the curves drawn.

In accordance with the present invention a continuous and accurate magnetic curve, such as a magnetization or hysteresis curve,

is traced directly by a beam of light on a sheet 0 of li ht-sensitive paper mounted on adrum revo at such a speed that the distance, by which any oint on the sheet of pa r moves to the rig t or left of an arbitrary hne parallel to the axis of rotation of the drum '80 is proportional to the variation of the magnetizing force, while the beain of light which is reflected from the mirror'of a deflecting fiuxmeter deflects at right angles to the direction of travel of the paper by amounts proportional to the total A ux produced in the sample by the varyin magnetizing forces.

The invention willie more readily understood from the following description and accompanying drawings in which:

Fig. 1 depicts in a schematic manner one embodiment of circuit arrangements and apparatus;

I Fig. 2 shows the electrical circuits in more detai Figs. 3 to fishow reproductions of hysteresis loops of various magnetic materials which were traced by an apparatus in accordance with the invention.

In Fig. 1 an elongated li ht sensitive cell 20 is mounted behind a V-siaped slot 21 of an opaque enclosure or box 22 m such a manner that light emanating from the l' ht source 32 and reflected by the mirror 23 astened to the moving coil 23 of the fluxnieter 24 falls upon the cell. The cell 20, in series with a battery 25, is connected to the fluxmeter 24 in parallel with the secondary winding 26 of the specimen 27. The current induced in the secondary winding of the s imen by the change in magnetizing orce caused by the change in intensity of the current flowingin the primary winding 28 tends to deflect the mirror of the fluxmeter. Current flowing in the circuit of battery 25 is proportional to the amount of light falling on the light-sensitive cell which amount, because of the we e-shaped ope is proportional to the de action of the uxmetermirror.

The voltage of battery 25 is adjusted to such a value that if the lig t beam is at rest when at the apex of the slit; at any other position, .the current passing through the cell will develop a torque in the fluxmeter coil which just balances the restoring torque of the suspension 50 of the fluxmeter Since the restoring torque and the amount of induced current are both proportional to the deflection, the resto torque is neutralized for all deflections an the fluxmeter deflections are directly proportional to the changes of E f electric cell 20, the value of potential applied a light tight box rheostat 36 flux occurrin within the secondary winding 26 under the influence of changes in magnetizing force of the primary winding 28.

In order to register the fluxmeter deflections and to vary the magnetizing force exerted by the primary winding 28, a drum 29 wound with photographic paper is placed in aving a long, narrow slit 31 parallel to the axis of rotation of the drum. A beam of li ht emanating from light source 19 is reflectef by the fluxmeter mirror, focused on the slit 31 and brought to a fine point by means of a lens 33 inserted in the slit 31. This beam is reflected by the same fluxmeter mirror 23 which reflects the beam onto. the hotoelectric cell, the two beams bein inci ent at difierent angles. Attached to t e shaft 34 of the drum is an arm 35 which slides along a rheostat 36. Battery 51 supplies the magnetizing current for the primary winding' it is connected across the and a center a 37 is soldered to the rheostat. Between e arm and the center tap a varying E. M. F. is produced which is applied to the primary or field coil 28. This E. M. F. reverses its sign every time the arm 35 slides past the center of the rheostat, and the latter is curved in a' manner calculated so that the.variation of thefield current will be proportional to the angle of rotation of the drum from the center position. When the drum 29 is rotated it moves the photographic paper past the slit 31 so that the distance moved is oportional to the variation of the field cu nt. The rotation of the drum 29 thus causes a correspondin variation of the magnetizing force exerted y the primary coil 28. A current is thus induced in the secondary coil 26, causing a deflection of the fluxmeter mirror 23. The fluxmeter mirror deflects the beam of ljilllt emanating from 32 along the slit 31. T 's deflection is proportional to the time integral of the changes of flux within the specimen. A curve with rectangular axes is thus registered on the photo aphic paper; the abscissa of this curve w ch is arallel to the direction of rotation of the may be calibrated in terms of magnetizing force and the ordinate which is parallel to the axis of the drum may be calibrated in terms of flux density. While the drum 30 may be rotated by hand, b means of knob 52, it is preferably rotated by an electric motor of constant s ed (only the pulley 53 is shown) geared own to about 1 revolution in two minutes, in order to insure a constant rate of rotation of the drum during the tracing of a curve.

' Fig. 2 shows the electrical circuits in detail. 37 represents the rheostat controlling the field current and 35 the arm which rotates with the drum 29 of Fig.1. The battery 25 supplies the magnetiz' current. -The battery furnishes the E.- F. for the phototo the latter being regulated by an adjustable resistance 40 not shown in Fig. 1. The potential divider 41 and dry cell 42, in series with a resistor 43 having a resistance of about 10 megohm, are provided for the purpose of balancmg out thermo-electric potentials and currents from the photo-electric cell due to stray light. The resistances 44 and 45 are adjusted according to the amount of flux already in the specimen at the be inning of the test in order to start the deifiection of the fluxmeter from the correct value. The mutual inductance 46, the current in the primary of which is ad ustable by resistor 56,

balance out otentials produced in the secondary coil 2% when no specimen is within it, thereby making the deflection of the fluxmeter 24 proportional to the change in flux density as a function of varying magnetizing forces. Resistor 55 serves to regulate the maximum in etizing current to which it is desired to sub ect the sample under investigation. Ammeter A measures the ,value of the magnetizing current at any particular time. igs. 3 to 6 depict reproductions of actual hysteresis loopstraced by an apparatus in accordance with the present invention. In these curves, the magnetizing forces, shown as abscissaa, were varied from a maximum negative value of 10 gauss to a maximum positive value of 10 gauss. .The ordinates re resenting flux densities are shown on different scales. 1

The material investigated and charted in Fig. 3 was very soft iron (about 0.15% carbon) It may be seen that the hysteresis loop, although very narrow, is regular and continuous The maximum flux density for the magnetizing force used was 7750 auss.

ig. 4 shows a similar hysteresls loop for a difl'erent material, namely, hard iron of a carbon content of about 0.80%. This hysteresis loo is rather wide, showing that this materi has a tendenc to retain all the magnetism induced in it. T e maximum induction was 14800 gauss.

Fi 5 and 6 show hysteresis loops for nicks and for one of the alloys known as permalloy containing 45% nickel and the balance iron, res actively.

What is c aimed is:

1. In a device for measuring variations in magnetic flux, rotatably suspended means, the suspension being sub 'ected to torsion and to a tangential restoring orce when traversed by an electrical current and means for counter-balancing the restoring torque of the suspension for all angles of deflection.

2. Device in accordance with claim 1 further characterized in this that the counterbalancing means comprise an electrically conductive path the conductivity of which is proportional to the flow of current in'the rotatable means.

3. In combination, primary and secondary windings, a source of current for said primary winding, two sources of light, a deflecting light reflector reflecting two discrete beams of light the angles of deflection of which are proportional to the current induced in the secondary winding under the influence of changes in the flow of current in said primary winding.

4. A magnetic testing device comprising rotatable suspended means responslve to variations of magnetic flux, means for integrating variations in flux density as timetions of varyin maignetizing forces, comprising means or e ectively compensating the restoring torque of the suspension for angles of rotation.

5. In a device for integrating and graphically recording changes in magnetic flux comprisin a suspen ed mirror type electrical in icating instrument deflected by changes in magnetic flux, a beam of light incident upon said mirror, means for counterbalancing the restoring torque of the suspension of said mirror comprising an electrically conductive path whose conductivity is a function of t e amount of light falling thereupon from the suspended mirror.

6. In a magnetic curve tracer, primary and secondary'windings adapted to surround a test sample, adjustable means adapted to subject the sample to a varying magnetizing force, means rotating an amount proportional to the variations of said magnetizing force, means rotating an amount proportional to the current in need in the secondary winding, deflecting means integral with said second mentioned rotating means and a beam of light reflected by said deflecting means for recording the deflection upon said first mentioned rotating means.

7. The method of ascertaining the variations in flux with magnetizing force of a body of magnetic material by means of apparatus includin a deflectable reflector suspended so that epartures from its normal position tend to set up a variable restoring torque which includes the steps of inducing a magnetic flux in the sample by means of an electric current, inducing an electric current by means of the magnetic flux, deflectin the reflector in accordance with the induce current and counterbalancing'the restoring torque for all deflections of said reflector.

In witness whereof, I hereunto subscribe my name this 29th day of Semmber 1930. FRANCIS E. WORTH. 

